1. Field of the Invention
The present invention relates to a video display control system for use in terminal equipment for a computer, television game apparatus or the like.
Recently, various kinds of display control systems which display animation and still images on a screen of a CRT (cathode-ray tube) display unit under the control of a CPU (central processing unit) have been developed. FIG. 1 shows one example of such conventional systems which comprises a video display processor (hereinafter referred to as "VDP") 101 and a central processing unit (CPU) 102. The system further comprises a memory 103 which includes a ROM (read only memory) for storing a variety of programs to be executed by the CPU 102 and a RAM (random access memory) for storing other necessary data. The CPU 102 outputs data representative of still and animation images to be displayed on a screen of a CRT display unit 105 to the VDP 101 which in turn stores the still and animation data into a video RAM (hereinafter referred to as "VRAM") 104.
Upon receipt of a display command from the CPU 102, the VDP 101 sequentially reads the still and animation data from the VRAM 104 in accordance with scanning synchronization signals of the CRT display unit 105, and supplies the read data to the CRT display unit 105, thereby the still and animation images being displayed on the screen of the CRT display unit 105.
In such a display control system, when the number of display elements or dots on the display screen is increased to improve the quality of a display image or when the number of bits of each color code is increased to increase the number of colors available, the quantity of data stored in the VRAM is also increased. As a result, the large quantity of data must be read from or write into the VRAM at a speed corresponding to the display speed so that the VDP must establish accesses to the VRAM at an extremely high speed.
However, in the conventional video display control systems, any particular means for making a high speed access to the VRAM have not been provided, so that it has been difficult to improve the quality of display image and to increase the number of colors available. In addition, in case of performing the access at a high speed, it has been necessary to use as the VRAM a DRAM (dynamic RAM) having a high access speed. However, such a DRAM is generally expensive.